The present invention relates to a thermoplastic resin composition having excellent weather resistance, impact resistance, fluidity, and gloss of molding, in which gas evolution during the molding is remarkably prevented.
This application is based on a patent application (Japanese Patent Application No. Hei 11-273462) filed in Japan, the content of which is incorporated herein by reference.
An improvement in impact resistance of resin materials is industrial useful because it increases uses of materials and makes it possible to reduce the thickness of molded articles and to enlarge the size of them. Therefore, various methods for improving the impact resistance of the resin materials have been studied.
As the material whose impact resistance was enhanced by using a rubber polymer in combination with a rigid resin, for example, ABS resin, high-impact polystyrene resin, modified PPE resin and MBS resin-reinforced polyvinyl chloride resin have already been employed industrially.
In particular, as the resin material having good weather resistance, using a saturated rubber component such as alkyl (meth)acrylate rubber is employed as a rubber polymer, for example, an ASA resin as a weather resistible ABS resin has been suggested.
As the method of preventing pearled gloss (pearled gloss defective) of colored molded articles as a drawback of the ASA resin, for example, a method of using a multi-layer crosslinked acrylic rubber containing a diene rubber in particles is suggested in Japanese Patent Application, Second Publication No. Sho 47-47863 and Japanese Patent Application, Second Publication No. Sho 59-49245.
Furthermore, a method of improving moldability and a method of improving balance between the gloss and impact resistance are disclosed in Japanese Patent Application, Second Publication No. Hei 3-66329. This publication suggests to use a composite rubber graft copolymer which contains a diene rubber enlarged by an acid group-containing copolymer latex in particles, and also has an outer-layer portion made of a crosslinked acrylate polymer obtained by using a graft-linking agent a crosslinking agent in combination.
Furthermore, Japanese Patent Application, First Publication No. Hei 10-77383 describes that a resin composition containing graft copolymer has good impact resistance by using a diene rubber which has a specific molecular weight of a toluene-soluble component, specific gel content and specific swell to toluene.
However, these prior arts do not describe with respect to gas evolution in case a resin composition containing a graft copolymer is molded, and gloss of molding in case molding conditions such as molding temperature are changed. The resin composition containing the graft copolymer prepared by the method of the Examples had the following problems. That is, a large amount of the gas is generated when the composition is molten and molded at comparatively high temperature and the gas adheres to the mold or resin surface, thereby to cause poor appearance such as poor gloss of the resulting molded article, and to be likely to make the working environment worse during molding. Although a technique of lowering a molding temperature, i.e. resin temperature, is generally employed to prevent the molding gas from evolving, it makes impossible to obtain a large-size or complicated resin molded article because of lack of fluidity of the resin.
That is, these resin compositions of the prior art had such drawbacks that they are hardly employed as raw materials of various molded articles because of very narrow molding conditions capable of maintaining the operation environment during the molding at good state and improving design of the resulting molded articles.
Therefore, there has not hitherto been found out any material which prevents the molding gas from evolving under wide molding temperature conditions and has good gloss of molding in the resin composition containing an alkyl (meth)actylate rubber, and it has been requested strongly to develop a technique which meets these requirements.
An object of the present invention is to provide a thermoplastic resin composition which prevents a gas from evolving during the molding on wide molding temperature conditions and exhibits good gloss of molding, and also has excellent weather resistance, impact resistance and fluidity.
The present inventors have intensively studied about the fluidity of a resin composition containing a specific graft copolymer as well as the amount of a gas evolved during the molding at high temperature. Surprisingly, they have found that a resin composition, which contains a specific graft copolymer and contains an emulsifier residue in a specific range, has good fluidity and causes less gas evolution during the molding at high temperature, thus accomplishing the present invention.
That is, the graft copolymer (G) of the present invention is a graft copolymer which is prepared by emulsion graft polymerization of a rubber polymer comprising 0-50% by weight of a butadiene unit and 50-100% by weight of a (meth)acrylate unit and at least one monomer selected from aromatic alkenyl compound, methacrylate, acrylate and vinyl cyanide compound, said graft copolymer containing 0.5-2.0% by weight of an emulsifier residue.